hagensick



Jan. 31, 1956 c. ca. HAGENSICK 2,733,400

RECTIFIER CONTROL APPARATUS Filed Jan. 19, 1953 7 Sheets-Sheet 1 Fig.|.

ll H2 Electronic Timer Control See Fig.2.

CON INVENTOR Charles G. Hagensick,

ATTORNEY Jan. 31, 1956 c. G. HAGENSICK 2,733,400

RECTIFIER CONTROL APPARATUS Filed Jan. 19, 1953 7 Sheets-Sheet 2 XY Z from Fiq.l.

m Peaking Fig.2.

5: I I I PS PS COIIfCIC T of Fig.|. |251 TSA l TSBI B -i' Contacts of Fig.l

-L- a-\ WITNESSES: PL Contact of Fig.1. INVENTOR Charles G. Hogensick.

BY 7% ATTORNEY Jan. 31, 1956 A c. s. HAGENSICK 2,733,400

RECTIFIER CONTROL APPARATUS Filed Jan. 19, 1953 7 Sheets-Sheet 3 SS-A F ss-a I50 VOLTS i0 2 2' 2 5 e 9 IO L s 9 I V i l I n \l Output-Voltage Components, of the Rectifier, Based on the A.C. Line-lo-Neulral I Voltages.

l F lg. 4.

I l 1 a I Plato-Voltage of the Charging-Tube CTl E58 2m 4 E Excitation-Circuit Voltages for the k 290 Ignite, 1| Grid- Voltage of lhe Charging Tube CTl Anode-Voltage of the Firing Tube FTI V 292 Resultant Excitation Voltage -30 E Firing Sine-Wave Sine-Wave Grid-Voltage 4%,, .4 0 k Components for the ATTORNEY Jan. 31, 1956 c HAGENSlcK 2,733,400

RECTIFIER CONTROL APPARATUS Filed Jan. 19, 1955 7 Sheets-Sheet 4 Equivalent D.C.Voltaqe Behind 5 Commutating Reactance (Unfiltered) 5 Instantaneous Load Voltage 2 Output-Voltage of the Rectifier, 7; (Fmered) s with Components based on the 5 f,

A.C Line-To-Neutrai Voltages lo :05 Tube Currents of the 5 1 Rectifier IO w p I '1 50s Pulse-Start for Tubes |,2,3,4

Portions of the Firing Sine-Wave Grid -Voitaqes Pu|se-Determ|n|ng Grid-Voltage 4 5 6 7 s 9 I0 II I2 I 2 Components for the Firing- Tube FTI I l I, l 1 1/1 I] 3'0 m2 312// l 1 3 I I I I 3 5' V BIT I I PL Opensl i -PL Closes 3 5 5 3|7 WITNESSES: Negative Blocking-Bios INVENTOR W Charles G. Hagensick.

ATTORNEY n- 31. 1956 c. G. HAGENSICK 2,733,400

RECTIFIER CONTROL APPARATUS Filed Jan. 19, 1953 7 Sheets-Sheet 6 Fig.8.

44 Peaking 355 Plate-Voltage of the Charging-Tube CTI E38 404 E38 396' E4! E43 f Grid-Voltage of the E 50 Charging-Tube CT! 402 392 R l-E335 kPeuking-Trcnsformer Pulse for OC=I20 l Voltage of the Firing Capacitor 38 s44 398 Grid-Voltages of he Firing-Tube FTI SO-I Zero Bias for OC=30 393 I T Charles G. Hugensick.

BY WW ATTORNEY 397 596 Last Instant of Release V of FTI Grld when OC=O Jan. 31, 1956 c, HAGENSlCK 2,733,400

RECTIFIER CONTROL APPARATUS Filed Jan. 19, 1953 7 Sheets-Sheet 7 (Asin Fig.8.)

Fig.lO.

Fig.ll.

Charging-Voltage (Transformer 4!) Anode-Cathode Voltage of the FiringTube FTI Charging Delaying Grid- Voltaga (Transformer 43) +Roleaso of Charging-Tube CTI L-Poaking-Transformor Pulse to Control OC=|50 l ,Firinq Sine-Wave (Transformer 44) 415 I Zero Bias for 426 c 60 I E54" 4.7 of k liasw o) INVENTOR Rectifiod Half Charles G. Hagenslckr 1 Sine-Wave ATTORNEY 2,7 33,4519 REtCTIFlER CQF ITRQL APPARATUS (Sharlcs G. Hagensielr, Pittsburgh, Pa., assignor to Wcst-= inghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Application January 19, 1953, Serial No. 332,if5 17 Claims. (Cl. 321--14) My invention relates to control-apparatus for rectifier circuits, including such features as a very rapid and flexible broad-range delayed-firing control, with or without the use of a firing-capacitor which is charged through a delayed-firing charging-tube; also, means for providing a gradual initial buildup of the output-voltage of the rectifier, when voltage is first applied to the output-circuit of the rectifier; and also special arc-suppression means, for protecting the rectifier.

A rapid changeable firing-angle is particularly needed when an unusually accurate control of the output-voltage is needed, or when it is necessary, for any other reason, to very rapidly change the firing-angle to any one of a number of adjustable points, over a considerable range of firing angles. in rectifier-applications which require only a slow speed of phase-shift of the firing-angle (such as a time of ten cycles or much higher), the required characteristics can be obtained with a mechanically moving phase-shifter, or with a type of firing circuit using a phase-controlling reactor having a variable amount of saturation. Phase-shifting delayed-firing controls have also been known, which have used grid-controlled firingtubes having one or more peaking transformers connected in the grid-circuit of the firing-tube, with means for rapidly changing the biasing voltage of this grid-circuit, so as to vary the effective position of the zero grid-control voltage, and thus vary the effective height of the peak or peaks.

An essential feature of my rapid, broad-range firingcontrol apparatus is the use of a sine wave for the tubefiring voltage in the grid-circuit of the firing-tube, and to control the point, along this sine-wave firing-voltage, at which the firing-tube is tired, by controlling the amount and the direction or polarity of the grid-biasing voltage. This combination can be used with or without any one or more of various auxiliary devices, such as a peairer, or a negative half-wave bucking-voltage, or a delayed firing of a charging-tube for charging a firing-capacitor which serves as the plate-voltage supply for the firing tube.

in many rectifier-applications, particularly high-voltage rectifiers which are used to energize electronic circuits, it is desirable to prevent the sudden application of the full rectifier output-voltage to the load-circuit, in order to prevent shock-excitation, and possible failure of the electronic equipment. There is a need, t erefore, for a means for slowing down the initial buildup of the outputvoltage of the rectifier, so as to require a certain length of time, such as four or five milliseconds, more or less, before the full steady-state output-voltage of the rectifier is applied to the load-circuit. A voltage-buildup curve which is similar to the first quarter of a 60-cycle sinewave is often suitable for this purpose. My present invention provides two alternative means for accomplish ing this end. One delayed-buildup means uses a rectifiercircuit having a large number of rectifier-tubes, only a few of which are initially fired, preferably by means of a synchronized pulse which is suitably synchronized with rates Patent lee 2,733, l lll the polyphase supply-voltage which is applied to the rectifier-tubes which are selected to be fired first. Another delayed-buildup means uses the previously described sinewave firing-voltage in the grid-circuit of the firing-tube for each of the plurality of rectifier-tubes, and provides a circuit including a suitable inductance for adding a positive biasing voltage to an initially blocked grid-circuit for each of the firing-tubes, so that the brid bias changes according to an exponential curve, because of this inductance, thus gradually decreasing the firing-angles of the rectifier-tubes.

In rectifier-equipments which are used for supplying loads which are subject to severe, frequently occurring, faults which amount practically to short-circuits on the rectifying equipment, it is quite desirable to protect the rectifiers during the time when the fault is being cleared, either on the alternating-current side or the direct-current side of the rectifier-s. One feature of my invention is therefore to provide current-transformers in the polyphase supply-circuits for the rectifiers, and to provide a rectii ed output from said current-transformers, with a means for using this rectified current-transformer output in an arc-suppressing means for incapacitating the control-circuit means (such as the firing tubes) of the several rectifier-tubes. In this Way, I am able to arequench the fault-currents very rapidly, thus minimizing the duty on the rectifier-tubes, and preventing or minimizing the development of arc-backs and other defects within the tubes.

With the foregoing and other objects in view, my invention consists in the circuits, systems, combinations, parts, apparatus, and methods of design and application, hereinafter described, and illustrated in the accompanying drawing, wherein.

Figure l is a considerably simplified drawing of an otherwise complete equipment, including circuits and apparatus, illustrating one form of embodiment or application of my invention, in form in which two parallelconnected protector-tubes or protector-tube circuits are used, in which the exciting anode of first one tube and then the other is fired, so that at least one of the tubes is carrying a holding-arc at all times, although neither one of the tubes carries such an are continuously,

Fig. 2 is a simplified diagram of circuits and apparatus indicating an electronic timer-control which is indicated by block-diagram in Fig. 1,

Fig. 3 is a time-diagram of certain features of the timercontrol,

Fig. 4 is a diagram showing exemplary waveforms and phase-relationships illustrating the excitation of the ignitor of one of the rectifier-ignitrons which are shown in Fig. 1,

Fig. 5 is a diagram showing exemplary illustrative waveforms and phase-relationships illustrating the initia- 'tion and ending of a single pulse of direct-current voltage on the power-line, with a gradual initial voltage-buildup according to a method in which only some of the rectifier tubes are fired at the very beginning of the pulse, accordto the control-equipment which is shown in Fig. 1,

Fig. 5 is a diagra .imatic view of circuits and apparatus, illustrating a. modified form of a portion of the equipment which is shown in Fig. l, whereby a gradual initial voltagebuildup is attained by rapidly changing the initial-delay of all of the rectifier-tubes during the buildup-period,

Fig. 7 is a diagram showing exemplary wave-forms and phase-relationships illustrating the gradual-buildup control of Fig. 6,

Fig. 8 is a simplified diagrammatic View of circuits and apparatus, illustrative of another example of the rapid broad-range rectifying-angle control for the grid-circuit of the firing-tube for one of the rectifier-ignitrons, distinguishing from Fig. l in showing a diagram in hich there is a 60-degree delay in the firing of the charging-tube which charges the firing-capacitor,

Fig. 9 is a diagram showing illustrative wave-forms and phase-relationships, illustrative of the firing-control equipment which is shown in Fig. 8,

Fig. 10 is a view similar to Fig. 8, showing a modification using only a 30-degree delay of the firing of the charging-tube after the zero value of the charging-voltage, and

Fig. 11 is a diagram showing exemplary wave-fore and phase-relationships illustrating the operation of the equipment shown in Fig. 10.

Fig. 1 shows an exemplary form of embodiment or application of my invention, in which a three-phase or other polyphase bus 13 supplies sixty-cycle energy, or other power frequency, to a group of twelve rectifierignitrons, numbered 1 to 12, which supply highvoltage direct-current energy, through a filter-reactor 14, to a direct-current power-line RA and RB, which energizes a load-equipment which may comprise any number of parallel-connected load-devices, such as L1 and L2, through individual ballast-resistances B111 and The load-devices L1 and L2, which are diagrammatically indicated by block-diagrams, are intended to be symbolic of any load-equipment which is subject to unpredictably occurring short-circuited conditions. In the actual circuit which is illustrated in Fig. 1, each of the load-devices L1 and L2 is the plate-circuit of a highvoltage high-vacuum radio-frequency oscillator-tube (not shown in detail). Such tubes are subject to flash-arcs, which are high-current discharges of short-circuit magnitude, resulting from an unpredictable failure of the insulation which the tube normally provides between its main electrodes, as described in such publications as a paper by Bailey in Proc., National Electronics Conference, 1948, page 127; a paper by Bell et al. in J. I. E. B, vol. 83, 1938, page 176; a paper by Gossling in l. l'. E. E., vol. 71, 1932, page 460; and a paper by Hansford et al. in I. I. E. 13., vol. 65, 1927, page 308. Repeated flasharcs of this nature cause gradual gas-evolution or a rise in gas-pressure within the tube, and a loss of emission. In order to protect such tubes, it is necessary to relieve them of their flash-arc currents within an extremely brief period of time, of the order of ten microseconds, or an even shorter period of time.

The rectifier-supplied direct-current buses RA and RE is protected by a primary or alternating-current circuit breaker 15, which is much too slow to protect a tube which develops a flash-arc.

As described and claimed in a companion-application of John L. Boyer and myself, Serial No. 332,036, filed January 19, 1953, 1 provide a suitable number of protector-ignitrons 11 to 41 which are connected to the power-line RA-RB, preferably at a point after the filterreactor 14, that is, at a point directly across the positive and negative load-circuit buses RA and RB. in the form of embodiment shown in Fig. 1, two of the protectorignitrons, 11 and 31?, are connected in parallel to each other, and the other two protector-ignitrons 2? and 4P are also connected in parallel to each other, and the two parallel-connected groups are connected in series, across the positive and negative wires PR1 and PR2, although it is to be understood that a single pair of parallelconnccted protcctor-ignitrons could be used, if it had a voltage-rating sufficiently high to reliably withstand the high voltage which is applied thereto.

In accordance with my invention, the rectifier-assembly 1 to 12 may be any suitable assembly of power-tubes having a control-circuit means, of any type which requires to be suitably energized before each conductingperiod of that power-tube, in accordance with the principles which will be described hereinafter. Because of the rugged .nature of ignitrons, and their ability to withstand heavy short-circuit currents, these twelve powertubes 1 to 12 are illustrated as sealed ignitrons, which have an anode 16, a pool-type cathode 17, one or more control-grids 18, an ignitor 19, and an exciting or holdinganode 20.

While the illustrated rectifier-equipment is not limited to any particular number of phases, it is illustrated as a twelve-phase system, consisting of two serially connected six-phase double-way rectifiers, each of which isequivalent to a three-phase full-wave rectifier, or a so-called three-phase bridge. The two six-phase double-way rectifiers are supplied from two power-transformers 21 and 22, having out-of-phase secondaries so as to produce lineto-neutral rectifier-phases according to a twelve-phase systern, with the successive phases numbered 1 to 12, corresponding to the numbers of the rectifier-tubes. The first power transformer 21 is illustrated as having a Y or star-connected primary 211, a delta-connected tertiary 21T, and a delta-connected secondary winding 215; while the other power-transformer 22 has delta-connected primary and secondary windings 22F and 228. In rectifierwork, it is convenient to refer to the line-to-neutral secondary voltages, as if the secondary transformers 21S and 225 were star-connected, rather than being deltaconnected (as in fact they could be), and these line-toneutral or star secondary-voltages have accordingly been indicated in dotted construction-lines.

The primary windings 21F and 221 of the two powertransformers are energized, through alternating-current reactors 23, and through a primary circuit-breaker 15, from the bus 13. Polyphase current-transformers 24 are also provided, for responding to the total three-phase current which is supplied to the rectifier-assembly. The odd-numbered rectifier-tubes 1, 5, 9, and 7, 11, 3, are energized from the secondary winding 218 of the first power-transformer 21, with the supply-phase 1 being connected to the anode of tube 1 and the cathode of tube 7, while the supply-phase 5 is connected to the anode of tube 5 and the cathode of tube 11, and the supplyphase 9 is connected to the anode of tube 9 and the cathode of tube 3. The six even-numbered tubes 2, 6, 1t), and 8, 12, 4, are energized in a similar manner from the secondary winding 225 of the second power-transformer 22.

It will thus be noted that there are four three-phase groups of rectifier-tubes, each of which acts as a threephase rectifier-assembly, in which, as each tube ceases to conduct current, it commutates or transfers its current to the next lagging phase or rectifier-tube in that threephase group. Thus, the three-phase group 1, 5, and 9 is positively energized from the secondary winding 21S, and it has its three cathodes connected to a common bus RP1 which is the positive output-bus of the entire rectifierassembly. The three-phase rectifier-group 7, 11, and 3 is negatively connected to the same secondary winding 21S, and it has a common anode-connection RN1. The three rectifier-tubes 2, 6, and 10 are positively connected to the other secondary winding 22S, and these tubes have a common cathode-terminal RPZ, which is serially connected to the common anode-terminal RNl of the group 7, 11, and 3. Finally, the three rectifier-tubes 8, 12, and 4 are negatively connected to the secondary winding 22S, and they have a common anode-connection RNZ which serves as the negative output-lead of the entire rectifierassembly.

The three-phase control-power for the various equipments is supplied from the bus 13 through a delta-delta excitation-transformer 25, which supplies power to an excitation-bus X, Y, Z.

The rectifier control-equipment for the rectifier-tube 1 is shown by way of example, and as being illustrative of the general nature of the equipments for the other rectifier-tubes. The circuits for the various grids, ignitors, and excitation-anodes of the several tubes, both rectifiertubes and protector-tubes, are indicated by the letters G, I and A, respectively, followed by the tube-designations.

The grid-circuit G1 for the rectifier-tube 1 is provided with a grid-cathode capacitor 26, a grid-resistor 27, and the potentiometer 28 of a negative grid-bias source, which is diagrammatically indicated by means of a battery 29, although actually such bias-sources are usually in the form of rectifiers (not shown), energized from the excitation-bus X, Y, Z. As is conventional in high-voltage ignitron-circuits, the grid-circuit G1 may also include the secondary of a coupling-transformer 31, the primary of which is connected in the circuit A1 of the excitationanode, so as to give the grid a positive impulse when the holding-anode or excitation-anode fires.

The excitation-anode circuit A1 of the rectifier-tube 1 is shown as including a current-limiting resistor 32, in addition to the primary winding of the grid-coupling and it is shown as being energized, through rectifiers 33, from two adjacent phases of an auxiliary excitation-bus SX, SY, SZ, which is energized, through an auxiliary delta-star transformer 34, from the main excitation-bus X, Y, Z.

The ignitor-circuit 11 for the rectifier-tube 1 is shown as being energized from an ignitor-coupling transformer 35 through a serially connected rectifier 36, the secondary circuit of the transformer being shunted by a rectifier 37 to provide a circuit for the reverse-currents which are induced in the secondary. The ignitor-coupling transformer 35 is energized by a capacitor-discharge circuit which includes a firing-capacitor 38, a sloping inductor 39, and a grid-controlled firing-tube FTI, the sufiix 1 indicating that the firing-tube FT is for the rectifier-tube 1.

is energized from the excitation-bus X, Y, Z. Thus, the negative terminal of the firing-capacitor 38 is connected to the star point of the six-phase star-connected secondary winding of the charging-transformer 41. The terminals of this six-phase secondary winding are connected to the charging-circuits C1 to C12 for the various rectifier-tubes 1 to 12, respectively, The charging-circuit Cll for the firing-capacitor 38 of the rectifier-tube 1 extends, through a current-limiting resistor 42, to the anode-circuit of a charging-tube GT1, the cathode of which is connected to the positive terminal of the firing-capacitor 38. The charging-tube GT1 is provided with a grid-circuit which is controlled by a grid-circuit transformer 43 which is energized from the excitation-circuit X, Y, Z through a switch A131.

According to my present invention, the firing-tube FTl is a grid-controlled tube or thyratron which is specially controlled in order to obtain very fast alteration of the rectifying angle of the rectifier-tube 1, to obtain a gradual initial voltage-buildup of the rectifier-assembly as a whole, and to obtain certain special features of arc-suppression in the rectifier-tube 1. The firingtube FTl has a grid-circuit FGE, which essentially contains a source 445 of substantially sine-wave firing-control voltage, a variable positive-bias source, such as a potentiometer 45 energized by a battery 3-6 through a switch A82, and a rapidly adjustable negative-bias source, such as a potentiometer 47 energized by a battery 43 through a switch A133. The negative-bias potentiometer 4-7 may be shunted by a ripple-smoothing capacitor 49, to make sure that the negative bias voltage is smooth, although this feature is not really necessary, especially when the biassource is a battery 3-8, as shown. As a matter of fact, the negative-bias potentiometer 47 may supply either a negative bias or a positive bias to the grid-circuit FGi of the firing-tube F'Tl, because this potentiometer is provided with two sliders, as shown, so that its polarity may be reversed.

The complete grid-circuit F61 of the firing-tube FT! may contain certain control-features other than the essential features just named. As shown in Fig. 1, this grid-circuit FGl serially contains one phase of a sine wave transformer-secondary 44, which is connected between the conductor F61 and the conductor H1. The secondary phase, which is the sine-wave firing-control source for this grid-circuit F531, is one phase of an openstar secondary-winding 44 of a sine-Wave impulsingtransformer 5'1, which has a delta tertiary winding SIT and a star primary winding 51F which is energized from an auxiliary excitation-bus X, Y, Z, which is connected to the main excitation-bus X, Y, Z through a switch AB i. The other secondary terminals of this transformer energizes the firing-tube gridcircuits for the other oddnnmbered rectifier-tubes, as indicated. The correspondsine-wave firing-control voltages for the firing-tube grid-circuits for the even-numbered rectifier-tubes are supplied by a sine-wave impulsing-transformer 52 having a delta primary 52F and an open-star six-phase secondary 52S.

Continuing the tracing of the firing-tube grid-circuit F61 beyond the conductor H1 in Fig. l, we come next to a ballast-resistor 53 which serves as a source of negative half-waves which are derived from a suitable secondary phase of a sine-wave impulsing-transformer 54, which is connected across the ballast-resistor through a rectifier 55. The sine-wave impulsing-transformcr 54 may be similar to the transformer 51, (except for a higher secondary voltage), having a star primary winding 54?, a delta tertiary 554T, and an open-star six-phase secondary winding 548, which furnishes the negative half-sine waves for the firing-tube grid'circuits H1, H3, H5, H7, HF), H11, for the odd-numbered rectifier-tubes. Another negative-half-wave impulsing-transformer 56, similar to the transformer 52, is provided for the firing-control of the even-numbered rectifier-tubes. The negativehalf-wave ballast-resistor 53, in Fig. l, is connected between the conductor H1, and a firin control conductor ln accordance with my invention, the firing-control circuit P1 of Fig. 1 is used as the terminal of a special starting-circuit, which includes a timing-switch make-contact TSA which is connected between this circuit F1 and a control-circuit conductor 57. As a matter of fact, the corresponding firing-control circuits F2, F3, and F4, for the next three lagging-phase rectifier-tubes, 2, 3, and 4, respectively, are all connected to the firing-control circuit Fit, so that all four of these consecutively numbered rectifier-tubes, 1 to 4, are fired simultaneously. These four rectifier-tubes are the minimum number of tubes which are necessary to establish a rectifier-circuit between the positive output-conductor RPl and the negative output-conductor RNZ, within the rectifier-assembly 1 to 12.

Later on, the rest of the rectifier-tubes will be fired, as will be subsequently described, and then, when the impressed voltage on the tube No. 1 declines, the current which was being carried by this tube will be commutated to the next lagging tube, No. 6, of the three-phase group 1, 5, and 9; and when phase, behind the tube 1, which is lower than the voltage which is impressed upon the next lagging tube, No, 6, of that three-phase group, 2, 6, and 10, then the current which was being carried by the tube 2 commutes to the tube 6, and so on. At first, however, according to my invention, only the consecutively numbered tubes, ll, 2, 3, and 4 are initially fired.

As a matter of fact, provision is made, in Fig. l, for initiating the energization of the direct-current powerline RA-RB, on the consecutively-numbered rectifiertubes 1, 2, 3, and 4, the first time the power-line is energized, and the second time using the next four consecutively numbered rectifier-tubes, 5, 6, '7, and 8, by means of a timer-switch make-contact TSB, which connects the control-circuit conductor 57 to the firing-control conductors F5, F6, F7, and F3. When the power-line is again energized, for a third time, the last four rectifier-tubes, 9, 10, 11, and 12, are initially energized, through the 7 medium of a time-switch make-contact TSC which is connected between the conductor 57 and the conductors Ffi to F12. For subsequent energizations of the powerline, the cycle is repeated. The time-switches TSA, T82, and TSC are a part of the electronic timer-control which will be explained in connection with Fig. 2.

The rectifier-firing control-circuit 57 is energized by the closure or" a pulse-starting contact PS, which connects the circuit '7 to the slider of the positive-bias potentiometer 45, under the control the electronic timer-control equipment of Fig. 2. As will be explained in connection with Fig. 2, the pulse-start contact PS remains closed for only some one or two milliseconds, or only long enough to initiate the firing of the four firing-tubes FTl, BT52, FTE, and FT E', or whichever other four tiring-tubes are being controlled through one of the time-switch contacts T SA, TSB, or'TSC.

The negative terminal of the positive-bias potentiorn eter 45 is indicated at 58, and this terminal is normally connected, through the make-contacts lAl and iAZ of two correspondingly numbered relays "9A1 and PAZ, to a control-circuit conductor 59. in Fig. l, the make-contacts PAT and are shown in their open, or deenergized positions, out when the apparatus is operating, the operating-coils PAi PAZ of these relays are both energized, so that both of these matte-contacts will be closed. This type of illustration is in accordance with the usual practice of illustrating all relays in their deenergized positius. The same relay-designation is applied to the oper. oil, and to all of the contacts, any given relay, as a means of convenient identificat on, and to indicate the correlation of the parts. The encr gization of the relay-coils P91 and PAZ will he subsequently described.

The control-circuit conductor 59 is connected, through a resistor 61, to a slider 62 on the previously described potentiometer at, which can supply either a positive or a negative hiasvoltage, according to its adjustment, although norrr ly it would be adjusted to furnish a negative grid-blast g voltage. The conductor 539 is also permanently connected to all twelve of the firing-controlling conductors Fl. to le through resistors 62A, 62B, and 62C, respectively.

As v ill be explained in connection with the electronic timer-control of Fig. 2, this control-apparatus is so equipoed that, soon after the closure of the pulse-starting time-switch contact PS, and while the four first-energized rectifiers i to 4, or to h, or 9 to 12, as the case may be, are still firing, a so-call d pulse-length contact PL is closed, which connects the control-circuit 52?, through a rapidly variable res 53, to the positive terminal e negative-bias potentiometer 47, thus applying to the control-circuit conductor 59, or at this conductor u, i gative (according to the adjustment), and thus opplyng a suitable positive or gridiring volta e, through the resistors 62A, 62B and 23C, to the firin circuit control-conductors F1 to for all twelve of the rectifier-tithes. The time dur'ig which the pulse-length conductor PL remains close-cl tetermines the length of the pulse, or of the period of energization, which is applied to the power-line LEA-RB.

The grid-biasing potentiometer 4! is provided with a second slide: as, which is connected to the negat've terminal QN of an arc'suppression resistor 6. The positive terminal Q? of the arosuppression resistor on is connected to the negative terminal of the firing-capacitor 5' 5, and to the cathode of the firing-tube FTIl, and also to the common star-point of the secondary of the chargingtransrormer 41, which p wers the chargin circuits C3 to C12 of all twelve of the charging-tubes CTl to CH2, thus meaning that the Q? conductors for the control-circuits of all twelve of the rectifier-tubes are connected together. These 1? cir are also all grounded, as indicated at 67.

The positive-terminal circuit QP of the arc-suppression resistor 66, in Fig. 1, is also connected to the cathodes of three arc-suppression thyratrons A, B, and C. The anodes of these three arc-suppression thyratrons A, B, and C are connected, through additional make-contacts PAl and PAZ of the previously mentioned relays PAl and lAZ, and also through a back-contact 33X of a resetrelay 31X, to the slider 68 of a negative-bias potentiometer 69, which is powered through a battery The negative terminal or" this negative-bias potentiometer 6 co nected to the negative terminal QN of the arc-suppression resistor 66.

The operating coil of the reset-relay is connected across the terminals Q1 and QN of said arc-suppression resistor so. This 31X coil is also shunted by a resistorca acitor time-delay circuit 7'2, which dela; the dropout ti e of the relay. The reset relay 31X may he designed to pick up within some four or cycles, or whatever other arc-suppression time may he required, for suppressing the arcs in the rectifier-tuhes l to 12. When this reset relay 31X piclcs up, it opens its hack-contact 31X in the plate-circuit 68 of the arc ression thyratrons A, B and C, thus removing the are ing 've bias from the resistor 66 in the grid-cit iiit or the firing-tube PTl. This also deenergizes the operating coil 33X of the reset relay, which permits this relay to drop out, in accordance with whatever dropout-time it has, thus reclosing its back-contact 31X and reconnecting the plate-circuits of the arc-suppression thyratrons A, and C, in readiness for another arc-suppressing ope ation.

An arc-suppressing operation is performed, for suppressing the arcs in the twelve rectifier-tubes l to 12, in the event of the application of a releasing grid-biasing potential to the grid-circuit of any one of the three arcsuppression thyratrons A, B, and C. The control-means for these arc-suppression grid-circuits will best be described after the rest of the apparatus of Fig. 1 has been described, and while the operation 01 the device is being described.

The control-circuits and connections for the protectorignitrons 1P, 2P, 3?, and 4P will new be described. The cathodes of theprotector-tubes i? and 3 are connected together, in a circuit PR1, which is connected to the nega tive rectifier-output circuit RNZ, and which is also connected to the negative power-lie conductor The common anode-circuits of these two protector-tubes 1? and 3? are serially connected to the common cathodecircuit PRO of the other two protector-tubes 2i and 4P, and an impulse current-transformer is connected in this series connection. The anodes the second two protector-tubes 2? and 4? are connected together in a common circuit PR2, which is connected to the positive power-line conductor RA.

A simplified version of the control-circuit, apparatus and connections for the two parallel-connected protectortubes 1F and 3? is shown in Fig. l, in sur'iicient detail for an explanation of the operation, with the understanding that similar controls can be used for the other pair of protector-tubes 2? and l-P, or this second pair of protectortubes may be omitted entirely, if each oi the tubes 1? and 3? of the first pair is capable of withstanding the outputvoltage of the rectifiers.

The ignitor-circuits L1? and L3? of the pr tectorignitrons 1P and 3P are fired alternately, on alternate halfcycles of the 60-cycle rectifier-supplying circuit 13, by means of a conventional reactor-ty e firing-circuit, consisting of a feed-transformer S l, a l i521 reactor $5, a firing capacitor 86, a saturable reactor 57, and rectifiers 83 and $9.

The excitation-anode circuits A-l? and A3? of these two protector-tubes 1P and 3 are each fed from two phases apart, in the illustrated embodiment), of a four-phase star-connected secondary winding El, through rectifiers 92. The transformer secondary 91 is energized from two primary windings 93 and 94 which are energized from an auxiliary four-wire excitation-bus PX, PY, P2,

energized from a delta-star transformer 95, which is in turn energized from the main excitation-bus X, Y, Z. The same auxiliary four-wire excitation-bus PX, PY, PZ, PO is also used to energize the feedtransforrner 84 for the ignitor-circuits I1P and I-3P.

The currents which are fed to the excitation-anode circuits A-1P and A-3P are limited, in each case, by two current-limiting resistors 96 and 97. Each of the resistors 96 is shunted by a small transformer 96' and a capacitor 98, for energizing a lamp 99 for providing a visual indication when the corresponding excitation-anode is periodically conducting, during successive periods of somewhat more than a half-cycle each. The other currentlimiting resistors d7 of the two excitation-anode circuits A-lP and A-3P are respectively shunted by transformers 101 and tea, the secondaries of which are connected so as to buck each other in an excitation-signal circuit having the terminals PR1 and FBI, which are used to energize an insulating transformer 103, which energizes the operating coil PAI of the relay PA1, and which is also used in connection with the arc-suppression control which will be subsequently described. As long as the excitation anodes A-IP and A-3P are being successively energized, in proper fashion, so that an exciting-arc is always playing in at least one of the parallel-connected protector-tubes 11 and 3?, the insulating transformer 103 will be properly energized, so as to maintain the excitation of the relay PAI.

In case a second pair of protector-tubes, 2P and 4P is used, as illustrated, there will be other excitation-signal terminals PR9 and P32, corresponding to the described terminals PR1 and FBI, for energizing and insulating transformer 14%. which energizes the operating coil of the relay PA2.

The control-grid circuits G1P and G-3P of the protector-tubes 1? and SP are normally negatively biased by block or prevent these tubes from breaking down when subjected to the output-voltage of the rectifier-assembly, even when the excitation-anodes A1P and A3P are conducting. Each of the control-grid circuits (3-11 and Cir-3P has a grid-to-cathode capacitor 105, and a series resistor 106, the latter being shunted by a capacitor 107.

The two grid-circuits G-lP and G-3P then continue, from a common conductor GPl, through a negative-bias branch, extending from said conductor GPl to the common cathode-circuit PR1, through a current-limiting resistor 110 and a negative-bias potentiometer 111 which is energized from a battery 112. The common portions of the grid-circuits G-IP and G-3P also have a positive-bias PG, which is in turn tors 107 which shunt the gri -resistors 106, so as to cause high initial grid-currents, which facilitate extremely rapid release of the protector-tubes IP and SF, in a matter of a few microseconds. The capacitors 107 which shunt the grid-resistors 106, provide high initial grid-currents for a few microseconds in the grid-circuits G1P and G-3P, for releasing the protector-tubes IP and 3?, while the gridcathode capacitors 105 serve to prevent release by shockover, or sudden application of anode-to-cathode voltages. These grid-cathode capacitors 105 should be as small as possible, in order that they will not prevent a high speed of release of the protector-tubes IP and 3P, respectively.

From the positive-bias ballast-resistor 113, the positive-bias branch continues through a back-contact RR of a reset-relay RR, and then through a grid-release thyratron GR to the common grid-circuit conductor GPI for the two grid-circuits G-IP and G-3P of the protectortubes IP and 3P.

The grid-release thyratron GR has shield and control grids which are connected, in parallel, to a common gridcircuit 120, which has a grid-cathode capacitor 121, a grid-resistor 122, a control-pulse insulating-transformer 123, and a negative-bias potentiometer 124 which is energized from a battery 125. The secondary winding of the control-pulse insulating-transformer 123, which is included in the grid-circuit 1263 of the grid-release tube GR, is shunted by a resistor 126.

The reset-relay RR is provided with an operating-coil RR which is connected across the current-limiting resistor through a resistor 127. If necessary, the opcrating-coil RR of the reset relay may be shunted by a capacitor 123 in order to secure a delay dropout-operation.

As described and claimed in the companion applica tion of Boyer and myself, I provide a high-speed faultdetection means. In Fig. l, a separate fault-detection means is associated with each of the ballast or buffer-resistors BR1 and 5R2, which are connected in series with the respective loads L1 and 12. As shown, the negative terminals of the butter-resistors BR]. and BB2 are each connected to the cathode of its own detector-thyratron D1 and D2, as the case may be. The grids of these detector-thyratrons D1 and D2 are provided with gridresistors GR1 and GRZ, respectively, which are connected to the bus RA through a common negativebias potentiometer 130, which is shunted by a filter-capacitor 131, and energized by a battery 132. The grid-circuit of each of the detector-thyratrons D1 and D2 receives a positive signal across its associated buffer-resistance BRl or BR2, as the case may be, when a load-current flows through that resistor.

In the event of a fault in one of the load-circuits L1 or L2, the voltage which is developed across the corresponding bias-resistor SR1 or 3R2 becomes much greater than the negative bias of the potentiometer 130, causing a rapid release of the grid of the associated detector-thyratron D1 or D2. The speed of this grid-release is increased by having the grid-resistors 6R1 and GRZ each shunted by a capacitor 133. The grid-circuits of the detector-thyratrons D1 and D2 have grid-to-cathode capacitors 134, which protect the thyratrons against shockover, or erroneous impulse-responsive firing as a result of sudden voltage-applications, but these grid-cathode capacitors 134 should be as small as possible in order to have a high rate or" release of the detector-thyratrons D1 and D2 in response to a fault in the associated load L1 or L2.

The anodes of the two detector-thyratrons D1 and D2 are connected to a common anode-circuit CQN, which serves as the negative terminal of a detector-pulse controlcircuit, the positive terminal of which is designated as through a positively charged capacitor 135, which is charged from a high-voltage source, such as a battery 136, through a large resistance 13?. When there is a fault in one of the loads L1 or L2, the voltage across its ballast-resistance ER1 or 8R2 assists the voltage of the positively charged capacitor 135?, and at the same time fires the corresponding detector-thyratron D1 or D2, so that the positively charged capacitor 135 is discharged, giving a fault-indicating control-pulse in the circuit CQP and CQN.

The detector-pulse control-circuit CQP used to energize an insulating transformer 141, having secondary terminals PR1 and PS1, which energize the control-pulse insulating-transformer 123 in the grid-circuit of the grid-release tube GR. When the second pair of parallel-connected protector-tubes 2F and t? is used, as illustrated, the detector-pulse control-circuit CQP and CQN will also energize a second insulating-transformer 142, having secondary terminals PRO and PS2 for performing a similar service for the protector-tubes 2P and 4P.

Attention will now be directed to the grid-control cirand CQN is ll. cults for the various arc-quenching tubes A, B, and C which are shown at the bottom of Fig. 1.

The left-hand arc-quenching tube B, as shown in Fig. 1, involves a novel overcurrent-control in accordance with my present invention. This overcurrent-control is obtained from the three-phase supply-line current-transformers 24, through a rectifier-bank 143, which provides a rectified output from said current-transformers, for energizing a current-transformer control-circuit CT? and CTN, which in turn energizes a grid-circuit potentiometer 144, having a slider 145 which is conn cted to the control-grid of the arc-quench tube B. The negative terminal CTN of the potentiometer 1 24 is connected to a negative-bias potentiometer l lo for the grid-circuit of said tube 8, this negative-bias potentiometer being energized from a battery 14 7. Thus, when the polyphase supply-current becomes suificiently large, as under faultconditions, the supply-line current-transformei's apply a sufficiently positive voltage to the circuit CT? to release the slider 14%, and hence the grid ot the ai'c-ouench tube B, thus firing this tube and applying the negative bias of the potentiometer 69 to the common circuit-portion Ql l of all of the grid-circuits of the firing-tubes, such as FTl, thus preventing any subsequent firing of any of the rectifiers 3 to 12 as long as the plate-circuit or" said tube B remains connected to the potentiometer 69.

As described and claimed in the companion application of Boyer and myself, the arc-quenching tubes C and A are controlled in various manners dependent upon the operation and control oi the protector-tubes 1? to 41.

The arc-quench tube C is released in the event of the loss of an excitation-arc in one or both of the parallelconnected protectontubes ii and SP, and, it the second pair of protector-tubes 2i and i? are used, then also in the event or" the loss of an excitation-arc in both of. the parallel-connected protector-tubes 2. and 4?. As previously explained, these excitation-arcs are needed, in the protector-tubes 1? to 4?, in order that load-fault protection may be available, that is, in order that the proteeter-tubes ii to may stand in instant readiness to be fired, by the release of their grids, in the event of a short-circuited condition on either one of the load-devices Li or L2. As previously explained, this fault-protection availability is indicated by the presence of a continuing voltage-signal in both pairs of control-lines PRl-PBE. and PKG-P52, which energize the respective insulatingtrans'f ners Hi3 and These voltage-signals, which appear in the secondary circuits of the insulating transformers N3 and tile, are rectified by rectifier-bridges 153 and 154, respectively, filtered by inductors 155 and capacitors 35b, and impressed on potentiometers 163 and 3.64, respectively, to pr negative in the grid-circuit of tie arc-quenching thyratron 3. This grid-circuit is also provided w th positive bias-voltage through a potentiometer led is energized from a battery tea.

The arc-quench thyratron A has its grid-circuit controlled so as to be responsive to a fault-detection signal, or to the releasing or the firing of suitable protector-tubes 1P to 4P. By way of example, two alternative grid-firing means are used in the grid-circuit of the arc-quenching thyratron A, one grid-firing means being used as a safeguard for the other, so that the tube A may be fired by the :JlCkiiSi possible means, in the event of a short-circuited condition on one of the load-devices L1 or L2, or in the event of the releasing oi the grids of the protector-tubes 31F to 4P, or in the event of the establishment of a load-shorting circuit through the bank of protector-tubes 1? to 4P. The fault-detector controlling-circuit pulse is taken from the previously described control-circuits CQP and CQN, and applied, through an insulating transformer 167, to a positive-bias poten"ornctcr 368 in the grid-circuit of the arc-quench: g thyratron A. in addition, the flow of a load-protect short circuiting current through the bank of protector-ignitrons ii to 4? is detected by the previously described, serially connected impulse-transformer 80, which energizes a control-circuit JQP and I QN, which,

in turn energizes a positive-bias potentiometer 169 in the grid-circuit of the arc-quench tube A. This grid-circuit is also provided with a suitable negative biasing-voltage, through a potentiometer 170 which is energized from the battery 171.

My invention is generally applicable to any rectifierinstallation in which a quick control of the rectifying angle is controlled by quick changes in the grid-bias in a grid-circuit which contains a substantially sinusoidal grid-firing voltage. The particular embodiment of my invention which is illustrated in Fig. 1 relates to a system in which the rectifier-tubes l to 12 are electronically controlled by a timer which produces a succession of short impulses, each having a duration anything up to seventyfive milliseconds, or 4.5 cycles of the 60-cycle supply, at a pulse-rate of anywhere from one to ei ht pulses a second, by way of example.

The electronic control-equipment is indicated by a block diagram in Fig. 1, and a simplified diagrammatic showing of this electronic equipment is given in Fig. 2. Some of the "features of the electronic timer-control which is shown in Pig. 2 were invented by R. B. Squires and I. B. Brittain.

The timing for the electronic control-circuits, as shown in Fig. 2, is synchronized with the oil-cycle rectifier-supply voltage by means of a three-phase bank of peaking-transformers 172, which are energized from the excitation-bus X, Y, Z of Fig. l, and which in turn supply a succession of positive and negative peaks to three secondary-circuits SA, SB, and SC, each of which contains a resistor 173, and the correspondingly lettered time-switch make-contact TSA, TSB, or TSC, as the case may be. The three secondary circuits SA, SB, and SC are then combined into a single circuit at 174, which is continued on, through a resistor 175, a conductor 1%, and a resistor 177 to ground. The conductor 176 is connected, through a resistor 173 to a synchronizing-signal bus SS, from which the electronic timer-control apparatus derives its initial controlling-impulses.

An arrangement is made, whereby the synchronizingsignal bus SS may be short-circuited in the event of conditions requiring arc-suppression in the rectifier-tubes i to 12 of Fig. 1. In the event of an arc-suppression operation, the reset-relay 31X of Fig. l is energized, and closes a make-contact 18%, which short-circuits the synchronizlug-signal bus SS, as indicated in both Fig. l and Fig. 2. The synchronizing-signal bus SS may also be shorted by a manually controlled switch ill-l, as shown in Fig. 2, or by a make-contact of a relay of the same designation, which will be subsequently described.

The electronic timer-control apparatus or" Fig. 2 comprises two time-base equipments, comprising tubes T2 to T5 and T2 to T5, respectively, operating under the control of the synchronizing-signal bus SS, and serving to produce, respectively, a long and a short saw-tooth wave, in output-circuits marked STL and STS, respectively. These saw-tooth waves are used to energize a group of electronic devices, or so-called electronic switches, whose contacts can be made to close and open, or open and close, at definite times, and for definite intervals, on a repetitive basis.

The various tubes of the electronic equipment of F a have their plate-circuits energized from a bus marked +250, while some of their cathode-circuits are connected to a grounded bus marked GND. The plate-circuit supply is obtained i'rorn a very accurately controlled voltage, which is simply indicated, in Fig. 2, as a plate-battery 182, although an elaborately controlled plate-voltage source is actually used, the details of which are not necessary to an understanding of the present invention. Some of the grid-circuits of the tubes shown are biased from an accurately controlled. grid-bias bus,.

araaaoo 13 trolled voltage-source, which is diagrammatically indicated by cans of a bias-battery 183 in Fig. 2.

The long-period time-base equipment T2 to T of Pig. 2 has a pentode T2, Whose control-grid (or simply grid) is controlled through a voltage-divider 134, 185, and res, which is connected between the synchronizingsignal bus SS and the grid-bias bus +150. The last element of this voltage-divider is preferably potentiometer, for the purpose of varying the amplitude of the negative signal which appears at the plate of the pentode T2, as will be subsequently described. The suppressor of the pentode T2 is connected to the cathode, and the screen is connected to the plate-supply bus +250 through a resistor 18?. The plate of this pentode is connected to the plate-supply bus +250 through a plate-resistor 183.

The pentode T2 is normally biased to cutofl. If a sufficiently large positive synchronizing-signal is applied from the shrty-cycle peaking-transformer 172 to the grid of this tube, the tube becomes conducting and a corresponding negative signal appears at the plate, due to the voltage-drop in the plate-resistor 188. if a negative signal is applied to the grid, the tube still remains in its cutofi condition. Hence, this tube operates to produce a negative peak, or a voltage-dip signal, at its anode, with an amplitude which is variable by the potentiometer 186.

During the normal cutofi condition of the pentode T2, its plate-voltage is +250 volts, the same as the platevolta e bus +250. This plate-voltage of the pentode T2 is applied, through a voltage-divider 190, 1%1, which applies a normal voltage of, say, +150 volts to the first grid of a double-triode cathode-follower tube T3. Hence, the cathode of the cathode-follower tube T3 is normally held at +150 volts, of which about 3 volts appears across a cathode-resistor 192, and about 147 volts appears across a serially connected cathode-capacitor 193, the latter being shunted by a high resistance 194.

If, now, a negative signal appears on the plate of the pentode T2, this attenuated and applied, as a negative pip, to the first grid of the cathode-follower T3, through the voltage-divider 19%), 191. This causes a corresponding drop in the cathode-voltage of the cathode-follower tube T3. However, the cathode-capacitor 193 is charged to about 147 volts, and hence the cathodevoltage cannot instantly drop below this value of about 147 volts. Hence, the cathode-drop is limited to a fixed value of about three volts, which is the proper amount for triggering the following stage of the equip ment. It is to be noted that this negative trigger of about three volts is independent of the magnitude of the signal which is given by the sixty-cycle peaking-trans former 1'72.

The second section of the cathode-follower tube T3 is connected as a diode, that is, with its grid connected to its plate. The two cathodes of this tube are connected together, so that the second plate of the tube is normally at +150 volts, corresponding to the normal cathodevoltage. This plate-voltage is tied to the plate of the next tube T4.

This tube T4 is a pentode, which is connected as a phanastron sweep-generator of a type which is similar, in principle, to that which is discussed in the M. I. T. Radiation Laboratory Series, vol. 19, pages 195-204. The plate of the phanastron tube T4 is connected to the plate-voltage bus +250 through a plate-resistor 195. The cathode is connected to the grounded bus GND. The sceen is connected to the plate-voltage bus +250 through a resistor 195. The suppressor-circuit 1971's connected to the screen through a resistor 198. The suppressorcircuit 197 is also connected to the negative bus +150 through a variable resistor 199.

The plate of the phanastron tube T4 is connected to the first grid of a double-triode cathode-follower tube T 5. The first cathode of this cathode-follower tube T5 is connected to the grounded bus GND through a cathode-resistance 204, and it is connected to the grid of the phanastron tube T4 through a timing-capacitor 205. The grid of the phanastron tube T4 is connected to the suppressor-circuit 197 of this tube through a highresistance circuit consisting of a resistor 206, a conductor and a resistor The conductor 2&7 is nected to the slider of a potentiometer 209 which is connected between the positive bus --250 and the grounded bus GND, and which normally holds the phanastron grid slightly positive with respect to the cathode, which is at ground potential. The grid is about volts positive with respect to the suppressor-circuit 197, but negative with respect to the first cathode of the cathode-follower tube T5, so that the timing-capacitor 2% is normally charged to a value which may be about volts, so as to present its negative terminal to the phanastron grid.

The suppressor-circuit 197 of the phanastron sweepgenerator is normally set so as to cut oil the platecurrent, so that the screen gets all of the current, and hence the screen-voltage is depressed by the voltage-drop in the screen-resistor 1%. When the three-volt negative pulse appears on the cathode of the preceding cathodefollower tube T3, it is transferred to the plate of the phanastron T4- through the diode section of the preceding cathode-follower tube T3. This causes the plate-voltage of the phanastron T4- to fall, and also the grid-voltage of the first section of the tube T55. The corresponding cathode of this tube T5 also falls, by cathode-follower action. Since the timing-capacitor 26 5 cannot discharge immediately, the drop in potential is transferred to the grid of the phanastron T4. This reduces the amount of current drawn by the screen of the phanastron, and hence the screen-voltage rises. There is a regenerative action, because the screen tied to the suppressor through the resistor 1 98, so that the suppressor-voltage also rises. This causes a plate-current to fiow in the phanastron T4, which further reduces the plate-voltage because of the voltage-drop in the plate-resistor 195.

This regenerative action continues, in the phanastron tube T4, until the plate-voltage drops very rapidly by a certain fixed amount of about five volts, in the illustrative example. The phanastron has now been triggered, and it subsequently operates according to its own law of action, until it resets its-elf, meanwhile being unaffected by any further triggering signals, because of the action of the diode section of the tube T3, until the completion of its resetting operation, which will be subsequently described.

at this time, the fivevolt drop in the plate-voltage of the phanastron T4 is communicated to the first grid, and hence to the first cathode, of the cathode-follower tube T5. Since the charge on the timing-capacitor 265 cannot change instantly, this also causes a depression in the grid-voltage of the phanastron T l. This grid-voltage depression is sulficient to carry the phanastron-grid negative, with respect to the suppressor-circuit 197 so that grid-current no longer fiows, and the total plate and screen current is very low.

The timing-capacitor 2% now begins through the high resistance 2%, which serves as a timingresistor for the timing-capacitor As the timing-capacitor 2%" gradually discharges, the grid-voltage of the phanastron rises linearly with time, and the plate-voltage or" the phanastron linearly falls. As this plate-voltage of the phanastron falls, the first cathodevoltage of the cathode-follower tube T5 also fails, following the phanastron plate-voltage. Since the first cathode of the cathode-follower tube T5 is tied to the phanastron-grid through the timing-capacitor 205, it keeps the grid-voltage of the phanastron T4 from rising too rapidly. This feedback is such that the timing-capacitor 295 discharges linearly.

The above-described discharging-action of the timingcapacitor 205, accompanied by a voltage-reduction on the first cathode of the cathode-follower tube T5, conto discharge tinues until the phanastron plate-voltage can go no lower. When this happens, the first cathode of the cathodefollower tube T can no longer hold the phanastron gridvoltage down. The phanastron grid-voltage then rises, increasing the total current drawn by the phanastron, but the phanastron-plate can draw no more current, and hence the phanastron-screen takes the increased current. This causes the screen-voltage of the phanastron T4 to fall, because of the voltage-drop in the screen-resistor 1%, and this in turn causes the suppressor-voltage to fall and to cut off the plate-current. The plate-voltage then immediately rises to its initial value of +150 volts, at which point it is held by the diode half of the preceding cathode-follower tube T3. This action takes place very rapidly, and results in a very rapid resetting of the entire system consisting of the tubes T2 to T5, holding the system in readiness to wait for the next synchronizing signal to repeat the process.

The high speed of resetting of the sweep-circuit generator T2 to T5 is brought about by the rapid recharging of the timing-capacitor 2% through the first section of the cathode-follower tube To". Without this section, the timing-capacitor 2&5 would have had to recharge through the rather large plate-resistor 195 of the phanastron tube T4, and hence the retrace or the reset-curve of the sawtooth voltage would be very slow.

The second section of the cathode-follower tube T5 is also connected as a cathode follower, with its grid connected to the first cathode of this tube. Thus, the second cathode of the cathode-follower tube T5 is directly connected to the long-period saw-tooth outputcircuit STL, and it is also connected to ground through a cathode-resistance 216. The second section of the cathode-follower tube T5 thus serves to isolate the output from the sweep-circuit, and it also provides a lowimpedance source for the output-circuit STL.

The long-pulse saw-tooth generator, or sweep-generator, consisting of the tubes T2 to T5, with the outputcircuit STL, has its circuit-constants adjusted, in the illustrated example, for a saw-tooth length or timing period of one second, or sixty cycles of a 60-cycle system.

There is also a second saw-tooth generator, or sweepgenerator, consisting of the tubes T2, T3, T4, and T5, and having a short-time saw-tooth output-circuit STS, in which the timing capacitor 2% is of a different size, and also some of the resistances are difier-ent, so that this second generator is set for a short time-base or sawtooth-length of 75 milliseconds, or 4.5 cycles of a 60- cycle system.

It is desired that, when the operation is first started, the two time-base sweep-generators shall start simultaneously, in response to the same impulse from the sixty-cycle peaking transformer in, as received on the synchronizing-signal bus SS.

it is also desired that, when the short-time-base sweepgenerator T2 to T5 resets itself, it will wait until the longtime-base sweep-generator T2 to T5 resets itself. To this end, it is arranged that the long-wave generator T2 to T5, when it first begins its down-swee ing voltage which constitutes the saw-tooth wave, shall operate a contact which will short-circuit the synchronous-wave bus SS, as indicated by the relay-contact 111%, which will be ubsequently described.

it further desirable to be able to change the length of the long saw-tooth-wave which is generated by the longtime-base generator T2 to T5, so that the pulserepetitions do not need to occur at the rate of one per second, but may occur at shorter timeintervals, down to intervals oi", say, one-eighth of a second. To this end, the long-period saw-tooth generator 2 to T5 is provided with a circuit which connects the phanastron suppressor-circuit T9? to the negative bus -l5tl through a relay make-contact RPiJ, which will be subsequently described.

In other respects, the two sweep-generators Til-T5 and T2'T5 are similar, so that a description of one will suffice for both.

Fig. 2 also shows simplified representations of certain electronic switches which are operated or controlled by the two saw-tooth wave-circuits STL and STS. Each electronic switch could consist of simply a tube or tubes, the conductive operation of which would correspond to a switch or relay contact-closing operation, while the locking of the tube or tubes would correspond to a contact-opening operation. However, in the actual application of my invention which has been chosen for illustration in Figs. 1 and 2, the various electronic switches consist of very fast, tiny, electronically controlled, electromagnetically operated relays, for example, relays havin tiny mercury-switch contacts, which have been schematically indicated as ordinary relay-contacts, as it is theoretically possible to use any kind of relaycontact which can be closed and opened with sufiicient rapidity, perhaps something like three or four millisecends, or less, if possible. By way of contrast, it may be noted that these electronic switch-operating times are something lilte 500 times longer than the few microseconds which are required to short-circuit the directcurrent power-line RARB by means of the grid-controlled protector-thyratrons ii to ll in Fig. l.

ince all of the electronic switches in Fig. 2 are alike, except for their potentiometer-adjustments, and with other exceptions which will be noted, a description of one will suflice for all.

The long-base timewave circuit STL controls two electronically operated repetition-period control-switches, having electromagnetically controlled relays which are marked RPa and Rib, respectively. Each of these electronic relays has its own double-triode cathode-follower tube T, having the two cathodes connected together, and connected to the negative bus -l5b through a cathoderesistor The first anode of each of these tubes T is directly connected to the positive bus +259 while the second anode is connected to said positive bus through the operating coil 1 3a or RPb of its associated electromagnetically operated repetition-period relay, as the case may be.

The first grid of each of these two iong-base-control tubes T of these electronic switches RPa and Rlb is connected to the long-base control-circuitSTL. The second grid of each of these tubes is connected, through a gridresistor 221, to an adjustable point on its own potentiometer 222, which determines the voltage-point, on the saw-tooth input-wave, at which the tube will become conductive, so as to energize its associated relay-coil. The potcntiometers 222 of the two electric switches which are controlled by the long-base saw-tooth circuit STL are energized from potentiometer-buses HPll and i-IP12, which are respectively connected t the positive bus +259 and to the grounded bus GND, through separately adjustable resistors 231i and 2.32, respectively.

The tube T of each electronic switch starts with its first grid, and hence its cathodes, at the initial or highest value of the saw-tooth sweep. As the saw-tooth voltage drops, the cathode-voltage drops with it. Nothing happens until the cathodes drop to a voltage which is approximately the same as the potentiometer-setting of the second grid, at which point the second plate begins to carry current, thus energizing the associated electromagnetically operated relay-coil, such as Ria and RH), as the case may be.

When the sweep-voltage reaches its lowermost value and resets, the second plate-current of the tube T cuts off very rapidly, so rapidly that a high voltage is induced in the coil of the relay. To retard the decay of current and reduce this induced voltage to a reasonable value, it is usually desirable to connect the second plate of each tube T to the grounded bus GND through a small damping-capacitor 233 and a damping-resistor 23 i.

The output of the second time-base equipment T2 to T is arranged so that the short-base saw-tooth controlcircuit STS controls five electronic switches, which are arranged, in 2, in the chronological order of their operation. in this case, the potentiometers 222 of these five switches are energized from their own potentiometerbuses Hll, HP2, which are excited by separately adjustable resistors and 2 2, similar to the adjustable resistors and 232 for the long-base potentiometer-buses Hill and HPIiZ.

in the order of their operation, the five short-base electronic switches consist of two pulse-start switches PS1: and PS1), a first pulse-length switch PLa, a so-called bias-control switch BC, and a second pulse-length switch PM). In each case, the designation which is used for the electromagnetically operated relay-part of the electronic switch is also used as the name to designate the entire electronic switch. The bias-control designation BC is a misnomer, so far as is shown in the very much simplified diagram of Fig. 2, arising from the fact that certain other functions, not here shown, and not necessary to an understanding or" the present invention, are also performed by the bias-control switch BC in the actual apparatus in which the present invention was used.

The pulse-start relay PS1: of Pig. 2 has a make-contact, which is also designated as 9801. The other pulse-start relay F5!) has a back-contact, designated PS1). These two contacts are connected in series with each other so that a circuit is made under the control of the a contact and broken under the control or" the I) contact. Together, the two pulse-start relay-contacts PSa and PSI; perform the function which is re resented, in Fig. l, by a single pulse-starting contact PS.

in like manner, the two pulse-length relays PLa and llib, in Fig. 2, have serially connected make and break 0 itacts, tLa and PLb, respectively, for performing the function which is designated simply as a pulse-length contact PL in Fig. l.

in the case of the electronic switches PSI) and PLb, which have back-contacts in series with make-contacts oi switches PS1: and PLa, respectively, in Fig. 2, it is desired to slightly delay the drop-out time of these switches. During the resetting instant, when the sawteeth wave is resetting itself, it is desired that the [7 contact should not reclose as a result of the deenergization oi the b relay, before the a contact reopens as a result of deenergization of he a relay. in this way, we avoid the momentary reclosure of the circuit containing the serially connected contacts a and b, when the corresponding relays a and I) are simultaneously deenergized. To this end, it is desirable to provide the electronic switches PSb and PM), in Pig. 2, with an additional time-delaying circuit whereby the second plate of the tube T is connected, through a resistor 243, to the slider of a potentiometer 244 which is energized between the buses and GND. This time-delaying circuit cooperates with the clamping-capacitor 233 to delay the drop-out times of the b relays PSb and PLZ; very slightly, such as by a matter or some three or four milliseconds.

The electronic timer-control equipment of Fig. 2 also includes three time-switch relays TSA, TSB, and TSC, and three auxiliary time-switch relays TSAl, TSBL and TSCl, which are energized from a direct-current stationbus, which is indicated at and These timeswitch relays can be put into service by the closure of a manually operated positive-circuit switch 24?, which energizes auxiliary positive bus 251.

After the closure or" the bus-switch 249, the operation of the various time-switches from TSA to TSCI is first started off by the closure of the electronic bias-control relay-contact EC. This BC-contact energizes a circuit from the auxiliary positive bus 251, and this circuit continues, through a back-contact 253 of the second timeswitch relay TSB, a circuit 254, and a back-contact 255 of the first time-switch relay TSA, to a circuit 256 which energizes the positive terminal of the operating coil TSAI, the negative terminal of which is connected to the negative bus The auxiliary time-switch relay -TSA1 immediately picks up and closes its make-contact which connects the negative terminal of the coil TSA to the circuit 2,56. The positive terminal of the coil TSA was already connected to the auxiliary positive bus 251, through the back-contact 257 of the second time-switch relay TSB.

However, the TSA coil is not immediately energized, ir -"ruse it is short-circuited by the circuit containing the contcts BC, 253 and 255. Hence, during the very first pulse of the electronic timing equipment of Fig. 2, the time-switches TSA, TSB, and TSC do not come into play, remaining deenergized. However, on all subsequent pulses of the electronic timing equipment, the timeswitches TSA, TSB, and TSC successively come into play, as will now be described.

At the end of the first short-period saw-tooth wave, the BC electronic switch is deenergized, thereby opening its make-contact BC in the circuit between the auxiliary positive bus 25?. and the conductor 252. This removes the short-circuit from across the operating coil TSA, so that the two operating coils TSA and TSAl are new connected in series, in a circuit containing the TSB backcontact 257. This energizes the first time-switch TSA, opening its back-contact 25'5, and closing its various make-contacts. in this way, the time-switch make-contact TSA, which is shown in Fig. 1, is closed, so as to make a connection between the circuits 57 and F1 of Fig. l.

Ordinarily, the electronic timing-equipment of Fig. 2 is put into operation, as by the closure of the positiveswitch 249, for some two seconds (or more) prior to the activation of the rectifier-tubes 1 to 12, as by the closure of the control-circuit switches ABI to A134. This allows time for the various tube-filaments to heat up, time for the first time-circuit pulse to have passed, and time for other functions that need not be here described.

Let us assume, now, that the rectifier control-circuits are energized, and that the first time-circuit pulse, which thereafter activates the rectifier-tubes 1 to 12, occurs at a time when the time-switch TSA is already in its energized condition. The end of the preceding long-base pulse of the saw-tooth control-circuit STL has deenergized the repetition-period switch RPa, thus removing the RH: short-circuit from the synchronizing-signal bus SS, as will be more fully described after the description of the circuit-connections has been completed. The energized time-switch TSA will have its top contact TSA closed, in the peaking-transformer secondary-circuit SA at the top of 2, thereby selecting phase A of the supply-circuit the phase for supplying a synchronizing-pulse to the electronic timing-equipment of Fig. 2.

When this phase-A synchronizing-pulse comes, the short-base saw-tooth wave commences another downward ep, and the electronic switch EC is again energized, a certain point in this sweep, but only after a powervoltage pulse has been started in the powenliue RA-RB of Fig. l, as will be subsequently described.

{)ontinuing my description of the time-switch controlequipnient near the bottom of Fig. 2, it will be noted that this closure or" the BC switch-contact again energizes the circuit f32-253-25d, and this circuit is now continued through a TSA make-contact 2533, which energizes the operating coil TSBE of the auxiliary time-switch TSBT, which in turn completes a circuit to the TSB coil, in a manner similar to that in which the TSAl relay completed a circuit to the TSA coil, the circuit of this TSB coil being completed through TSC back-contact 259. The

coil is at first short-circuited by the circuit containthe switch-contact BC, so that the TSB coil does not become energized until the end of the short-period sawtooth pulse which has been holding the electronic switch closed. The TSB coil is thereupon energized, and

its back-contact 257 deenergizes the TSA coil, so that the first time-switch TSA is now deenergized, and the second time-switch TSB now stands energized, in readiness for the next power-pulse. The energization of the second time-switch TSB also opens its back-contact 253. The TSB switch also closes a make-contact 261 which connects the positive terminal of the coil TSCT to the circuit 252 in readiness for the next operation of the electronic switch BC.

The next saw-tooth pulse of the electronic equipment starts a power-voltage pulse under the control of the time-switch TSB, and after this power-pulse has been started, the electronic switch BC again closes, and energizes the operating coil of the auxiliary time-switch relay TSCl through the TSB make-contact 261. The closure of the auxiliary relay TSCI establishes a circuit for the TSC coil, which contains a back-contact 2&2 of the first time-switch relay TSA, but this TSC coil is at first short-circuited by the circuit containing the BC contact, that is, before the BC contact opens. When the BC contact opens, at the end of the short-base saw-tooth pulse, the time-switch relay TSC is energized, thereby conditioning the circuits for the beginning of the next voltage-pulse on the power-line RA-RB of Fig. 1. The closure of the relay TSC opens its back-contact 259, which deenergizes the coil of the time-switch relay TSB, and the time-switch relay TSB, upon deenergization, recloses its back-contacts 253 and 257, and reopens its make-contact 261, thereby resetting the time-switch control-circuits of Fig. 2, in readiness for a repetition of the operation.

Thus, after the time-switch TSC has controlled the initiation of another power-voltage pulse on the powercircuit of Fig. 1, the electronic switch BC again closes, while the power-pulse is still in progress, and this time, the BC contact energizes the auxiliary time-switch relay TSAl, through the circuit 252-253254-255256. This auxiliary relay TSAl again picks up, but again nothing happens until after the opening of the electronic switch BC, at which time the first time-switch TSA is again energized, and by opening its back-contact 262 it deenergizes the third time-switch relay TSC, thereby conditioning the time-switch circuits for another powerpulse, in which the time-switch TSA will be in control at the moment of starting of the power-pulse.

Before starting a description of the operation of the apparatus shown in Fig. 1, it will be helpful to make a brief reference to the operation of the electronic circuits of Fig. 2, with the aid of the time-curves which are shown in Fig. 3.

At the beginning of the operation, the voltages of the saw-tooth output-circuits STL and STS of both the longperiod and short-period time-base equipments in Fig. 2 are at their maximum value of +150 volts, as indicated in Fig. 3. At a moment 27% indicated by the first synchronizing signal SS-A, in Fig. 3, both saw-tooth waves are triggered ofi, so that the voltage quickly drops to 145 volts, as indicated by the point 271 in Fig. 3. After this, the two saw-tooth voltage-waves continue to fall, at different slopes, as indicated by the slanting lines marked STS and STL in Fig. 3. The short-time saw-tooth wave STS completes its downward sweep, to its lowermost voltage, which may be 108 volts, as marked, in a time of .075 second, or 4.5 cycles of a 60-cycle system, until the point 272 is reached, at which time the short-base saw-tooth voltage practically instantly rises to its initial value of +150 volts, as indicated at 273.

Meanwhile, the long-base saw-tooth wave STL, starting from the same point 271, continues its more gradual downward sweep, and, it it were uninterrupted by the second repetition-period switch RPb, it would continue on to its lowermost voltage, such as 100 volts, at the point 274, in a time-period which is indicated as one second or sixty cycles of a 6G-cycle wave. If the long-base sawtooth wave STL is permitted to reach this extreme lowermost point 274, it substantially instantly resets to its original voltage-value of volts, as indicated by the point 275 in Fig. 3.

At an early point in the downward sweep of the longbase saw-tooth wave STL, and if desired, even before this wave completes its first five-volt drop to the point 2 1, the first electronic switch RPa triggers, as indicated by the point Rla in Fig. 3. Next, in time-sequence, come the triggering of the electronic switches P511, PSb, PLa, BC, and PM), at successive points along the short-base saw-tooth wave STS, as indicated, by way of example, in I' l" it will be recalled, from the description of Fig. 2, that when the first repetition period switch Rla closes, it short-circuits the synchronizing-signal bus SS, so that no more synchronizing signals can be received over this synchronizing-signal bus until the release of the switch Rla, which occurs at the moment when the long-period saw-tooth signal STL resets itself. Thus, when the shortperiod saw-tooth signal STS resets itself at 272+273, in Fig. 3, it is not triggered off, to commence another short-period saw-tooth wave, until after the long-period wave resets itself, so that both saw-tooth waves can then be retriggered at the same moment.

At some point during the downward sweep of the longbase saw-tooth wave STL, in Fig. 3, the second repetitionperiod switch RPb is triggered, at some such point as indicated at RBI: in Fig. 3, just by way of giving an example. The effect of the closure of the electronic switch RPb, in Fig. 2 is to interrupt the discharging of the timing-capacitor in Fig. 2, so that the long-base phanastron tube rs immediately resets itself, so that the output-voltage, which appears on the long-base output-circuit STL of Fig. 2, rises substantially immediately to its initial voltagevalue of +150 volts, as indicated by the point 276 in Pig. 3. During the resetting process of this long-base sawtooth wave STL, the electronic switches RPa and RPb reopen, so that the switch Rla removes its short-circuit from the synchronizing-signal bus SS of Fig. 2.

Meanwhile, the time-switch group, which is shown near the bottom of Fig. 2, has reset itself, so that the timeswitch TSA is no longer closed, but the timeswitch TSB is closed. In Fig. 2, it will be seen that the top contact of the time-switch TSB, near the top of 2, now selects the supply-phase B of the 60-cycle supply-line, for furnishthe peaking-transformer peak which will be applied to the synchronizing-signal bus SS in Fig. 2.

Thus, in Fig. 3, when the first positive peaking-transformer peak occurs on the synchronizing bus of Fig. 7., after the point 276 in Fig. 3, a timer-triggering pulse will be received, at the point marked 88-13, at which time the two saw-tooth waves STS and STL will start down again, in a repetition of their timing operation.

it will be understood that each of the electronic switches has a millisecond adjustment, under the control of its gridcircuit potentiometer 222 of Fig. 2, so that it can be made to respond at any desired voltage-point, and hence at any desired time-point, along the saw-tooth wave which controls that particular switch.

While I have shown an exemplary electronic t1mercontrol, as shown by Figs. 2 and 3, I wish it to be understood that any other type of relaxation-oscillator saw-tooth generator could have been used, or any other types of switches which are responsive to the voltages of the sawtooth waves, or in fact other types of grid-bias controllingequipment for the grid-circuits of the firing-tubes, such as the firing tube 5T1, for the rectifier assembly, or for any other equipment for controlling the application of power to the direct-current power-line RA 3 in Fig. 1. it is believed, however, that the operation of my invention will better be understood by the inclusion of a showing of some precise, concrete circuit in which my invention is applied, and for which it was primarily designed and intended, as has been done in Figs. 1 to 3, although, of course, my invention is not limited to the precise circuit or application which has been chosen for illustration.

The eifect of the electronic timer-control of Figs. 2 and 3 on the power-tubes or rectiiientubes 1 to 12 of Fig. 1 is to cause the rectifier-tubes to deliver, to the power-line RA-RB, a succession of short power-pulses, with long intervals in between. The time between successive pulses is controlled by the long-base saw-tooth control-circuit STL of Fig. 2, and by the voltage-setting of the second repetition-period switch RPb which controls the resettingpoint of the long-base saw-tooth wave. Successive sawtooth pulses are started at predetermined points in synchronism with peaking-transformer pulses in successive phases of the three-phase power-supply bus 13, under the control of the top contacts of the three time-switches TSA, TSB and TSC of Fig. 2. The starting and stopping of the power-pulses which are delivered by the rectifier-tubes are controlled by the short-base saw-tooth control-circuit STS of Fig. 2, and by the respective voltage-settings of the first pulse-start switch PSI: and the second pulse length switch PLb in Pig. 2.

The operation of the rectifier-tube assembly which is shown in Fig. i will be better understood with reference to the time-curve diagrams of Figs. 4 and 5, wherein Fig. 4 shows the continuing operation of the rectifier, once the rectifier-operation has been started, while Fig. 5 shows the starting and stopping of a single pulse, by means of rectitier-control, together with the output-voltage of the rectifier-tubes.

The wave-forms of Fig. 4 are in three parts. The upper part shows some of the sine-wave input-voltages i to 12 for the correspondingly numbered rectifiers 1 to of F i, plotted on a time-base datum-line 283. The

c g periods of the various rectifier-tubes are indit by heavy lines, showing that the load carried by the tube 9 begins to commute to the tube 1 at the point 281, and finishes its commutation at the time 2S2282', While the tube 1 thereafter commutes to the tube 5, and the tribe 5 commutes to the tube 9, after which the process is continued. This shows the operation of the lowermost group of three-phase rcctifiers 1, 5, and 9 in Fig. 1, these rectifiers being positively connected. The operation of the negatively connected three-phase group of reetifiers 7, ii, and 3 is also shown in Fig. 4, wherein the load carried by the tube 11 begins to comniutate to the tube 3 at the point 25o, and finishes that commutation at the time 2o 284, after which the No. 3 tube commutates to the No. 7 tube, and the No. 7 tube commutates to the No. 11

tube. The corresponding operation of the other two three-phase groups of rectifiers in Fig. l is shown in Fig. 4, by dotted lines. The internal output-voltage of the en tire assembly of rectifier-tubes 1 to 12, that is, the recoutput-vo-ltage neglecting commutating and filtering reactances, is always, at any instant, the sum of the four heavy-line output-voltage components which are shown in the top portion of Pi 4.

Ti end portion of Fig. 4, using a time-base datunr shows the excitation-circuit voltages for the of the first rectifier-tube 1, in Figure l. in lg-capacitor 33 of Fig. l is indicated as at charged to the voltage At the ini ti rectifier-ignite!" i is fired, the firing a e and continues its discharge until the the capacitor swings to a negative stored energy in the sloping inductor the reactance of the ignitor-transiormer 35 in lvieanwliile, the anode-voltage of the firin -tube s a stepped shaped somewhat shown at EFTI The firing-capacitor 33 thereafter holds its 've charge until the point 292 is reached, in Fig. 2, -ding to the time 292' at which the charging'tube F ll and grid-voltage E43 become posi- 'e, reierrr 3 to the charging-tube GT1 in Figure l. The or thereupon begins to charge, according to exponential curve, during which time the anodevoltage of the firing-tube FTI gradually rises until, at some such point as 2.93, the capacitor 38 becomes sub- 22 stantially fully charged again, ready for another firingoperation.

The bottom portion of Fig. 4, using a time-base ti 1, shows some of the voltage-components in the grid-circuit FGl of the firing-tubc FT of Fig. l. The sine-wave ng voltage, which is furnished by the transformer g. l, is indicated at in Fig. 4, while the negative half-wave of sinusoidal voltage, which is impressed across the resistor-terminals 53 in Fig. 1, is indicated in Fig. 4 at E53, and the resultant of these two voltages is i dicated g. 4 at EFTI, indicating the resultant exition-voltage on the firing-tube grid-circuit P61 in Fig. l.

The resultant direct-current grid-biasing voltage which is impressed upon the firing-tube grid-circuit of Fig. 1, between the points QP and F1, is indicated, by way of example in Fig. 4, as being a negative bias Err, which is plotted, reversed, in Fig. 4 (that is, the bias voltage EF1 is plotted), so that this negative bias-voltage may be reg: rded as simply raising the datum-line G T up to the value EF1. At the point, therefore, where the resultant excitation-voltage EFGi becomes positive with respect to the shifted datum-line --EF1, as shown at the point 281 in Fig. 4, the firing-tube FTI is fired, causing this tube to apply the positive voltage E38 of the firing-capacitor 38 to the ignitor I1 of the first rectifier-tube 1 in Fig. 1, thereby firing said first rectifier tube and commencing the commutation-period which is indicated at 281232 in the top portion of Fig. 4. In this firing-process, as shown in Fig. 4, the firing-circuit delays are (correctly) assumed to be small enough to be negligible, or too small to be shown on the time-scale which is used in Fig. 4.

Fig. 5 shows some of the wave-forms for a single pulse of power, as delivered by the rectifiers it to of 1, showing the beginning and ending of the pulse. The actual filtered load-voltage, which is delivered to the power-line RA in Fig. 1, is indicated at ERA in the top portion of Fig. 5, plotted on a timebase datum-line 300. The equivalent direct-current rectifier-voltage, behind (or neglecting the filtering-effect of) the commutating reactance and the reactance of the filter 14 of Fig. l, is indicated in Fig. 5 by the curve E+.

At the moment when the pulse is started, in Fig. 5, rectifier-tubes are released at the same instant: the positively connected tube 1 and the negatively connected tube 4 are released at the point 301 in Fig. 5, while the posi- 2 and the negatively connected tube 3 are released at the point 302. In the case which has been chosen for illustration in Figs. 1 and 5, this releasing-time is 45 after the zero 303 of the No. 1 line-toneutral voltage 1, or 15 after the conventional 30-degree crossing-point 304 for simple three-phase rectifier-operation at which the declining phase-voltage 9 is crossed by the next-lagging, increasing, phase-voltage 1. At the instant of firing, therefore, the respective tubes 1, 2, 3, and 4 thus have ignition-angles of 15 delay, 15 advance, 45 advance, and advance, respectively, with respect to the normal zero-delay rectifier-point. For the initial release-operation, and before the remaining rectifier-tubes 5 to 12 are fired as will be subsequently described, the initial conduction-periods for the tubes 2, 3, and 4 are abnormally long, because of the advances in their firingangles.

The middle portiori of Fig. 5 shows the currents which are supplied by the several rectificrs 1 to 12, plotted, for convenience, on two separate time-bases 305 and 306, and showing the commutation-periods as the time be tween the instant 307 (for example) when the rectifiertube 5 first begins to carry current, and the instant 308 when the next leadin rectifier l, of this three-phase group 1, 5, 9, ceases to carry current after having transferred its load-current entirely to the tube 5. No commutatingcurrent bias, having some such value as 311 in Fig. 5. time was required in the initial current-carrying periods of the first-fired tubes 1, 2, 3, and 4, because no current shown at the moment 314-314,

or close to zero,

that the successive firing-circuits of the twelve rectifier- 23 was being carried by their next-leading associated threephase tubes at the moment of firing.

The lower portion of Fig. shows some of the pulsedetermining components of the grid-voltage of the firingtube FT]. of Fig. 1, plotted on a time-base datum-line 310. Before the commencement of the pulse, the gridcircuit FGl of the firing-tube FTI had a negative direct- This negative blocking-bias, which is applied between the grid-circuit points QP and 59 in Fig. 1, is so large that none of the sinusoidal grid-firing voltages 1 to 12 of the transformers 51 and 52 in Fig. 1 can fire their associated firing-tubes, such as tube FTl. (It will be observed that only a portion of each of these sinusoidal grid-firing voltages 1 to 12 is shown in Fig. 5.)

At a certain time-instant 312-312, in Fig. 5, the pulse-start contact PS of Fig. l (or PSa of Fig. 2) closes, thereby impressing, on the first four firing-circuits F1 to F4, the positive bias-voltage 312' of the biassource 35-46 in Fig. 1, assuming that the time-switch TSA stands closed, as described in the explanation of Fig. 2. This brings the negative grid-circuit bias 311 up to some fairly large positive bias-value 313, which is large enough to make sure that the firing-tubes (such as FTl) of the four rectifier-tubes 1, 2, 3 and 4 will fire instantly, thereby firing the ignitors and establishing an exciting-arc in all four of the rectifier-tubes 1, 2, 3 and 4.

1n the illustrated example, in Fig. 5, the ignitor-firing moment 312' occurs very slightly before the pulse-start moment 313', which is the moment when the instantaneous sum of the impressed voltages on the four rectifier-tubes 1, 2, 3 and 4 passes through zero in changing from negative to positive. Thus, referring to the sinusoidal voltage-components at the top of Fig. 5, before the pulse-start moment 301 the positively connected tube 1 had a smaller positive voltage than 301, while the negatively connected tube 4 had a larger negative voltage than 391, so that the sum of these two voltages was negative. In like manner, before the pulse-start moment 392 the negatively connected tube 3 had a larger negative voltage than 3E2, while the positively connected tube 2 had a smaller positive voltage than 3&2, so that the sum of these two voltages was also negative. Thus, the firing-tubes (such as FTI) of the four rectifier-tubes 1, 2, 3 and 4 fired the respective ignitors, and caused exciting-arcs to be established on the auxiliary anodes, a short while he fore the instantaneous sum of the four impressed voltages became positive, so that these four rectifier-tubes stood in readiness to fire as soon as their voltage-sum became positive, or at the instant 312, 302, 361. In this manner, a power-pulse is started, with only the first four rectifier-tubes 1 to 4 carrying current.

A very short while after the ignitor-firing time $12-$12, as shown at the bottom of Fig. 5, the starting-pulse is removed from the firing-tube grid-circuits, as by the opening of the PS contact in Fig. 1, or the PSb contact in Fig. 2. This again applies the strong negative blocking-bias 311 to the firing-circuits F1 to F4, but this has no effect upon the firing-tubes, such as FTl, because these firing-tubes are thyratrons, or gas-filled tubes, in which the gridcircuit has no power to interrupt the firing of the tube, once said firing-operation has been started. Furthermore, the condition of the firing-tubes (such as FTI) could have no efiect upon the corresponding rectifier-tubes 1 to 4 after their holding-arcs have been established, or, as in the illustrated example, after their main arcs have I been established.

At a certain subsequent time 315, a positive directcurrent bias-component 315-615 is applied to all twelve of the firing-circuits F1 to 512, by the closure or the pulse-length contact PL in Fig. 1, or PLa in Fig. 2. This makes all of the firing-circuits F1 to P12 of Fig. 1 have a total direct-current grid-circuit bias which may be Zero, as shown at the bottom of Fig. 5, so

that my apparatus tubes will thereafter proceed to operate in the manner which has already been described in connection with Fig. 4. The time-instant 315315 when the PL-contact closes in Fig. 1 (or the PLa-contact in Fig. 2), should be after the pulse is started by the firing of the first four rectifier-tubes, and before the zero-delay point for the phase succeeding the phases of these four rectifier-tubes. More strictly speaking, it is desirable, in the particular twelve-phase rectifier-installation which is represented in Figs. 1 and 5, that the phase position of the closing of the contact PL shall be in the 60 interval between an instant which is 45 after the pulse-starting instant 312, and an instant which is after said pulse-starting instant, as shown at 316 just under the upper portion of Fig. 5. Preferably, for the sake of safety, it is desirable to have this PL contact-closing time well within this interval, as indicated at 315 at the bottom of Fig. 5, or even at some somewhat earlier point.

The twelve rectifiers 1 to 12 continue to fire, in their normal manner, until a time-instant SIT-317, as indicated at the bottom of Fig. 5, at which time the PL contact opens in Fig. l (or the PM) contact in Fig. 2). From this time on, the four rectifier-tubes which were carrying current at said moment continue to carry current until their total combined input-voltages add up to zero, there being no more firing of rectifier-tubes after the time-instant 317'-317. The pulse is finally ended, at the instant 318 when these last four rectifier-tubes finally cease carrying current.

In the pulse-determining operations which are illustrated in Fig. 5, it will be observed that the equivalent internal direct current output-voltage of the rectifier-assembly 1 to 12 is equal, at any instant, to the sum of the lineto-neutral input-voltages of the four rectifiers which are carrying the load at any instant, using average voltages during the commutatiug-periods, such as the one which is shown, in the upper curves of Fig. 5, at 319. It will be observed that the effect of firing only tour of the rectifier-tubes at the start of each pulse or each energization of the power-line RA--RB in Fig. 1, is that the voltage-curve of the pulse rises more or less gradually, along a curve which approximately corresponds to the first quarter of a sine-wave of the frequency of the rectifier supply-circuit 13. This is a valuable feature of my invention, in reducing the shock which would have been imposed on the high-voltage load-devices L1 and L2, if they had been suddenly impressed with the full highvoltage output of the rectifier.

From the operational explanations which have been given in connection with Figs. 4 and 5, it will be evident as shown in Fig. 1 involves a firingangle control-means which, in its barest essentials, involves a sinusoidal grid-firing voltage-source 44, and means for applying various direct-current grid-biasing voltages, as at 66, 47, 63, 45, and'the electronic timer-control con tacts PS and PL of Fig. 1. These direct-current gridbiasing means may be changed, either manually or automatically, as slowly or as rapidly as may be desired or required, afiording a means whereby the firing-angle of the rectifiers may be obtained at any point along the sinusoidal grid-firing voltage, over a wide range including both positive and negative values oi said sinusoidal wave. The electronic switches PS and PL are examples of means for very rapidly changing the grid-circuit bias of the various tiring-tubes such as the firing-tube FTlt for the rectifier-tube 1. The arc-suppressor tubes A, B. and C also constitute electronic means for rapidly controlling the direct-current grid-bias voltage which is efi'ective in the grid-circuit of the firing-tubes, such as the tube 5T1. The potentiometers 35, 47, and ea constitute means whereby the firing-point may be manually selected or controlled, by controlling the amounts of the grid-circuit biases. The resistance 63 which is in series with the pulse-length contact PL, may be varied, either manually or automatically, either slowly or rapidly, as a means for controlling the firing-angle, and hence the output-voltage of the rectifier, so as to obtain any desired voltage-characteristic, under either manual or automatic control.

Various other features of my invention will be illustrated and described in connection with three alternative forms of embodiment, which are shown in Figs. 6, 8, and 19 respectively.

Fig. 6 is directed to a modification of the apparatus shown in Fig. l in which, instead of initially firing only four of the rectifier-tubes, in order to obtain a gradual buildup of the output-voltage of the rectifier-assembly, all of the rectifier-tubes are fired, and the value of the direct-current output-voltage during the buildup-period is controlled by rapidly changing the ignition-delay, by grid-bias control, during this buildup-period. Thus, the apparatus of Fig. 6 omits the electronic pulse-starting switch PS and the time-switches TSA, TSB, TSC of l, and substitutes, serially connected in the gridcircuit F61 of the firing-tube FTI, a grid-circuit resistor 3235, which is shunted by a positive-bias circuit contain ing a potentiometer 325, the electronic pulse-length control-contact PL, which has already been described in connection with Pi s. 1 and 2, and an inductor 325, which serves as a means for obtaining an exponential biaschange by introducing any required amount of delay in the buildup of the positive grid-biasing voltage-component in the grid-circuit F61 of the firing-tube FT The positive-bias potentiometer 325 may be energized from any suitable direct-current voltage-source which is represented by a battery 326.

The firing-grid circuit FGl of Fig. 6 also contains a variable-voltage grid-biasing potentiometer 327, which is shown, by way of example, as supplying a positive voltage-component to the direct-current biasing-voltage of the gridcircuit F61, although it is to be understood that the grid-bias could have been varied either up and down by this means, that is, that the variable-voltage grid-biasing potentiometer 327 could be used to introduce either a positive or a negative variable voltage-component. This potentiometer 327 is energized by means of a battery 328.

This potentiometer 327 in Fig. 6 has a slider 330 wlich is shunted by a voltage-regulator 331, which is indicated by block-diagram in Fig. 6, and which may be used, either under electromagnetic, electronic, or other control, to introduce a variable amount of short-circuiting resistance across the potentiometer 327 in response to the diifcrence between the rectifier output-voltage, such as the voltage across the power-line RA-RB, and a constant direct-current reference-voltage 332. This voltage-regulator 331, in- Fig. 6, thus serves as a means for rapidly controlling the grid-bias of the firing-transformer BT31, and hence as a means for rapidly varying the firing-angle, and hence the output-voltage of the rectifier-assembly l to 12, by changing the firing-point at which the sinusoidal firing-voltage of the source 44 makes the firing-tube grid FGi positive with respect to the firing-tube cathode QP.

in addition to the sinusoidal grid-firing voltage-source the Pig. 6 circuit also includes the source of negative sinusoidal half-waves, as shown at 53, 54, and 55, as described in connection with Fig. 1. Fig. 6 dififers from Fig. 1, however, in having the firing circuit Fit, for the No. l rectifier, connected to the corresponding firingcircuits to P12 for all of the other rectifier-tubes, that all of the rectifier-tubes will be fired simultaneously, or, more accurately, all of the other rectifiertubes will have their firing-controlling means simultaneously biased so that each firing-controlling means will be ready to fire when its sinusoidal firing-voltage becomes able to apply a positive resultant grid-voltage to the corresponding firingtube, such as the firing-tube FTl.

in addition to all of the above-described grid-controlling equipment, the firing-grid circuit FGl of the firing tube FTT in Fig. 6 also contains a peaking-transformer 335, which is suitably energized through a manually adjustable phase-shifter SH. This peaking-transformer is designed to apply a positive grid-biasing impulse at substantially the positive crest value of the sinusoidal grid-firing voltage of the source 4-4, for the purpose of increasing the range of firing-control by making it possible for the firing-angle to be adjusted (by direct-current grid-bias) so it occurs at substantially the crest of the firing-controlling sinusoidal voltage-wave, as will be subsequently described.

'lne amaratus shown in Fig. 6 also has different phaseangles for the excitations of the grid-circuit transformer 43 in the grid-circuit of the charging-tube CTZ, and the negative half-wave sinusoidal voltage-source 54 and the sinusoidal grid-firing positive-voltage source 44 in the gridcircuit of the firing-tube FT These alternating-current sources or transformers, in Fig. 6, are energized from an auxiliary excitation-bus UX, UY, UZ, which is energized from a star-delta transformer 33%, which derives its energy from the excitation-bus X, Y, Z of Fig. l, or from an X, Y, Z bus having similar phasing, which is supplied by means or" a star-delta excitation-transformer 339, which is indicated, in Fig. 6, as being energized from the anode-terminals of the rectificr-tubes Ti, 5', and 9. Otherwise, the apparatus which is partially shown in Fig. 6 is, or may be, identical with that which is shown in Fig. l.

The operation of the pulse-controlling aspects of my invention, as shown in Fig. 6, will best be understood by reference to 7. This figure contains three sets of voltage-curves, which are plotted, with different voltagescaies, on three different time-base datum-lines 341, 342, and respectively, the same time-scale being used in each case.

in the top portion of Fig. 7, the jagged line 1, It, 2, 3, etc., represents the equivalent theoretical internal directcur-ent rectifier-voltage, not counting the voltage-smoothing effects of the commutating or filtering reactances, with the plain-numbered points 1, 2, 3, etc., indicating the points at which the correspondingly numbered rectifiertubes are fired, and with the primed points 3, 4 5, etc., indicating the ends or" the coinniutating-periods at which the correspondingly numbered rectifier-tubes took over all of the load-current from the next leading rectifier-tube in that three-phase group. I am here referring to the four three-phase groups which are shown in Fig. 1, nameiy, fr, 5, 9; 7, El, 3; 2, 6, it); and 8, i2, in this top portion of Fig. 7, the twenty-kilovolt line represents the desired steady-state output-voltage of the rectifier, while the dotted lines, represening a plus or minus four er-cent voltage-variation, represent the tolerable voita variation which is peri itted by the voltage-regulator 3; in this particular installation.

to 12 of the corresponding y numb l (or Fig. 6). The no ions oft input-voltage waves during which the rcspectiv {.LtbfiS are c nducting current, as well as the volt during the comtnutating-periods, are indicated by h lines in 6, in a manner similar to that which has ready been shown and described in connection with Fig The bottom portion of Fig. 7, which is b. the datum-line 36-3, shows portions of the sinuso grid-firing voltage-waves PG to F812,

p'essed, the transformer 54, on t r tr l which c firinggrids or" the tiring-tubes for the correspondingly mun red rectifiers it to 12. At the crest of each of these sinusoidal firing c-ltages, is shown somewhat idealized peakingtransformer voltage-impulse E335, such as is supplied by the peaking-transformer 335 in Fig. 6.

In tially, before the pulse-starting switch PL closes, in Fig. 6 (or Pisa in Fig. 2,) there is a certain negative direct-current bias on the grid-circuits of all of the firing-tubes, such as the tube PTl in Fig. 6. This is shown, reversed, in the bottom portion of Fig. 7, as the 

